1. Field
Certain aspects of the present disclosure generally relate to wireless communications and, more particularly, to a method of designing a signal (SIG) field of a transmission preamble for signaling number of spatial streams per client combinations.
2. Background
In order to address the issue of increasing bandwidth requirements demanded for wireless communications systems, different schemes are being developed to allow multiple user terminals to communicate with a single access point by sharing the channel resources while achieving high data throughputs. Multiple Input Multiple Output (MIMO) technology represents one such approach that has recently emerged as a popular technique for next generation communication systems. MIMO technology has been adopted in several emerging wireless communications standards such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard. The IEEE 802.11 denotes a set of Wireless Local Area Network (WLAN) air interface standards developed by the IEEE 802.11 committee for short-range communications (e.g., tens of meters to a few hundred meters).
A MIMO wireless system employs a number (NT) of transmit antennas and a number (NR) of receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS spatial streams, where, for all practical purposes, NS≦min{NT,NR}. The NS spatial streams may be used to transmit NS independent data streams to achieve greater overall throughput.
In wireless networks with a single Access Point (AP) and multiple user stations (STAs), concurrent transmissions may occur on multiple channels toward different stations, both in the uplink and downlink direction. Many challenges are present in such systems.
Robust multi-user (MU) MIMO reception requires that the AP transmits all training sequences to the user STAs. The training sequences allow each STA to estimate a channel from all AP antennas to the STA's antennas. The STAs use the channel from all AP antennas to perform effective interference nulling from MU-MIMO streams corresponding to other user STAs. In order to perform robust interference cancellation at each of the STAs, each STA is required to know which spatial stream(s) belong to the STA and which spatial stream(s) belong to other STAs in the network.